ABSTRACT: Unraveling food webs is a first step toward understanding of ecosystem functioning and a requirement to forecast climate-induced ecosystem responses. In this study, the organisms under examination were benthic copepods (order Harpacticoida) inhabiting a fjord-like environment on the southern coastline of King George Island at the northwestern tip of the Antarctic Peninsula, one of the most rapidly warming regions on Earth. Despite increased understanding of Antarctic food web structures, little is known about the feeding ecology of benthic copepods in these systems. A fatty acid trophic marker strategy was used to unravel the diet composition of Antarctic harpacticoid copepod species or assemblages collected from distinct habitats in summer. Their diverse storage fatty acid composition revealed the occupation of different trophic niches associated with their specific lifestyles, i.e. endobenthic or epiphytic with (Alteutha spp.) or without (Harpacticus sp.) frequent water column excursions. Moreover, the prevalence of biosynthesized ω7 long-chain monounsaturated fatty acids in Harpacticus sp. and ω9 fatty acids in Alteutha spp. further suggested adaptations to particular habitats in polar ecosystems, as different dietary precursors—16:1ω7 (microphytobenthos, epiphytic diatoms) or 18:1ω9 (flagellates)—fuel these elongation pathways.